Somatotropin is a polypeptide secreted by the anterior pituitary in warm-blooded animals and acts through specific cell surface receptors located primarily in the liver (Hughes, J. P. and Friesen, H. G., Ann. Rev. Physiol., 47, 469-482 (1985)). Somatotropin is useful to enhance growth of such animals as bovine (cattle), porcine (pigs), caprine (goat), avian (chicken, turkey, geese, etc.) and rabbit, among others. Somatotropin is also useful to enhance the growth of other vertebrates, such as fish.
Specifically, the growth hormone pST is native to swine and accounts for maturation of the animal, including increasing the growth rate and the lean to fat ratio. It has been found that pST is a single chain polypeptide of 191 amino acids with two cystine bridges linking residues 53-164 and 181-189, respectively (Abdel-Meguid, S. S., et al., Proc. Nat. Acad. Sci., 84, 6434-6437 (1987).
Because endogenous amounts of pST are small, efforts have focused on the preparation of exogenous pST for use in large-scale agriculture. Efforts have also been directed to the identification of small portions of the pST molecule, the generation of antibodies to those portions, and the administration of those antibodies together with pST to enhance growth. See, for example, published European Patent Application 284,406.